A photocurable resin composition can be used for microfabrication by applying the principles of photography (photolithography). Further, since a cured product with excellent physical properties can be given, it is used for electronic devices, printed boards, or the like.
A photocurable resin composition includes a solvent development type and an alkali development type. From the viewpoint of environmental measures, an alkali development type allowing development with weak and dilute aqueous alkali solution is mostly used. For example, an alkali development type photocurable resin composition is used for production of a printed wiring board, production of a liquid crystal display panel, or production of a printing plate. When it is used as a solder resist for production of a printed wiring board, for example, the cured product thereof is required to have reliability characteristics like heat resistance to endure high temperature treatment like soldering, resistance to non-electrolysis gold plating, electrical properties, and PCT resistance. As a photocurable resin composition which satisfies, at least to some extent, resistance to migration and resistance to hot-cold cycle as a cured product, a photocurable resin in which many double bonds are introduced to a resin skeleton by using a polyfunctional epoxy resin or (meth)acrylate among carboxyl group-containing epoxy (meth)acrylate is used. It is believed that crosslinking density is increased according to such constitution, and therefore an improvement in heat resistance or dimension stability can be obtained.
Meanwhile, since a cured product becomes brittle as the crosslinking density increases, there is a problem that a balance between heat resistance and brittleness reduction is difficult to obtain. To deal with brittleness reduction problem, a method of using a mixture of bisphenol type carboxyl group-containing epoxy (meth)acrylate and Novolac type carboxyl group-containing epoxy (meth)acrylate is suggested (for example, see Patent Literature 1). However, the method focuses on an improvement of flexibility, and therefore it has a problem that dimension stability with changes in temperature or water resistance cannot be obtained at sufficient level.
According to an increase in the size of a board to which it is applied or to achieve a further improvement in production or the like, a resin composition having higher sensitivity is required in recent days. A polymer compound having a radical polymerizable vinyl group in the side chain can undergo a crosslinking reaction via polymerization of the side vinyl group to enable high-speed curing, and therefore an improvement in sensitivity is expected (for example, see Patent Literature 2 or the like). However, there is also a problem that it is not compatible with alkali developability.